The reproductive system provides the mechanism for the recombination of genetic material that allows for change and adaptation. Manipulation of this system in breeding management programs allows the rapid and dramatic alteration of the conformation and productivity of domestic animals. Theriogenology is the veterinary clinical specialty that deals with reproduction.
Sex determination of the gonads is important for development of the sex phenotype (internal and external genitalia, secondary characteristics) and sexual behavior. A sex chromosome genotype of XY leads to the development of testes due to the sex-determining region of the Y chromosome (SRY) gene. The SRY gene induces downstream factors such as SRY-box containing gene 9 (SOX9), anti-Müllerian hormone, and glial cell line–derived neurotrophic factor in Sertoli cells.
Abortion is the artificial termination of pregnancy after organogenesis is complete but before the fetus is viable. If pregnancy ends naturally before organogenesis, this is called early embryonic death. A full-term fetus that is delivered dead is a stillbirth, confirmed by lack of any indication of inflation of the lungs. Many causes of abortion can also cause stillbirths, premature or medically and physically compromised neonates, and occasionally mummified fetuses.
Bovine genital campylobacteriosis is caused by either Campylobacter fetus venerealis or C fetus fetus. Clinical signs include irregular estrous cycles, prolonged breeding seasons, and occasional abortions. A vaginal mucus agglutination test can be used for diagnosis but requires sampling multiple cows. Outbreaks can be controlled by vaccination or artificial insemination.
Brucellosis is caused by bacteria of the genus Brucella and is characterized by abortion, retained placenta, and to a lesser extent, orchitis and infection of the accessory sex glands in males. The disease is prevalent in most countries of the world. It primarily affects cattle, buffalo, bison, pigs, sheep, goats, dogs (All.see page Brucellosis in Dogs), elk, and occasionally horses. The disease in people, sometimes referred to as undulant fever, is a serious public health problem, especially when caused by B melitensis.
Contagious agalactia is caused primarily by Mycoplasma agalactiae and affects sheep and goats. The most common clinical signs are mastitis, conjunctivitis, and arthritis, although these are rarely observed in the same animal. Diagnosis depends on laboratory testing. Vaccine efficacy is variable, and animals should not be vaccinated during an outbreak.
Among domestic animals, cystic ovary disease (COD) is most common in cattle, particularly the dairy breeds, but it occurs sporadically in dogs (All.see page Follicular Cysts in Small Animals), cats, pigs, and perhaps mares.
Equine coital exanthema is a benign venereal disease of horses caused by equine herpesvirus type 3. Clinical signs include multiple, circular, red nodules on the genitalia of both mares and stallions. Diagnosis is based on clinical signs and can be confirmed by identifying the virus histologically. There are no vaccines or specific treatments. Sexual rest is recommended to allow lesions to heal and prevent spread.
Mastitis, or inflammation of the mammary gland, is predominantly caused by bacterial pathogens and occasionally mycotic or algal microbes. Pathologic changes to milk-secreting epithelial cells from inflammation decreases function, ie, milk production. Depending on the pathogen, deceased milk production may continue into further lactations, which reduces productivity and, for beef and other meat-producing animals, potential weight gain for suckling offspring. Although most infections result in subclinical local inflammation or mild clinical cases, more severe cases can lead to agalactia or even profound systemic involvement, including death.
In all species, acute puerperal metritis occurs within the first 10–14 days postpartum. It results from contamination of the reproductive tract at parturition and often, but not invariably, follows complicated parturition. Important causative organisms in cattle include Escherichia coli and Trueperella (Arcanobacterium) pyogenes, but culture-independent studies have demonstrated the dominant role of gram-negative anaerobic bacteria such as Prevotella melaninogenica and Fusobacterium necrophorum. The condition is usually acute in onset. Affected cows, mares, ewes, does, or sows are depressed, febrile, and inappetent. A fetid, watery uterine discharge is characteristic of the condition in cows but may not be conspicuous in other species. Milk production is diminished, and nursing young may show signs of food deprivation.
Two common and distinct forms of posthitis and vulvitis are recognized in small ruminants. The first, referred to as enzootic posthitis and vulvitis, is associated with high-protein diets, infection with Corynebacterium renale or other urease-producing organisms, locally high concentrations of ammonia, and severe posthitis. The second is referred to as necrotic or ulcerative balanoposthitis and vulvitis. Its cause is unclear, but Mycoplasma mycoides mycoides is implicated, as are other Mycoplasma spp organisms of the Histophilus/Haemophilus group, and potentially viruses, such as caprine herpesvirus 1.
The prevalence of postpartum dysgalactia syndrome (PDS), and mastitis in general, tends to be underestimated in swine herds, although it has been reported to be as high as 15%. Clinical signs are nonspecific and vary; it is often characterized by neonatal issues, and can be challenging to identify. PDS can be an economic burden and may reportedly cost producers up to 555 USD (€470) per affected sow, according to a 2017 Finnish study. For More Information see 1. Additionally, the pain and discomfort associated with PDS make it a welfare concern for affected sows.
Parturition is induced by the fetus in both cattle and sheep. It is initiated by rising cortisol levels in the fetus that provoke a cascade of endocrine activity in the dam. Fetal cortisol increases as a result of increased adrenocorticotropic hormone (ACTH) production by the maturing fetal pituitary caused by fetal stressors such as hypoxia and hypercapnia. Gestation length is unique to each fetus, but approximate gestation lengths can be ascribed to each species ().
Pseudopregnancy in goats most often affects older, parous does. The primary clinical sign is hydrometra, accumulation of fluid within the uterus. The condition can be diagnosed by ultrasonography or by finding low levels of pregnancy-associated glycoprotein. Treatment is a luteolytic dose of prostaglandin F2alpha.
Retention of fetal membranes, or retained placenta, usually is defined as failure to expel fetal membranes within 24 hr after parturition. Normally, expulsion occurs within 3–8 hr after calf delivery. The incidence in healthy dairy cows is 5%–15%, whereas the incidence in beef cows is lower. The incidence is increased by abortion (particularly with brucellosis or mycotic abortion), dystocia, twin birth, stillbirth, hypocalcemia, high environmental temperature, advancing age of the cow, premature birth or induction of parturition, placentitis, and nutritional disturbances. Cows with retained fetal membranes are at increased risk of metritis, displaced abomasum, and mastitis.
Seminal vesiculitis is inflammation and/or infection of one or both vesicular glands. Signs may include purulent material contaminating bull semen. Diagnosis often occurs during a breeding soundness examination through manual rectal palpation or visible observation with rectal ultrasound of enlarged seminal vesicles. Treatment includes broad-spectrum antibiotics to control local infection and NSAIDs to reduce inflammation. Bulls with persistent or recurring seminal vesiculitis are considered unsatisfactory breeders and should be culled.
Trichomoniasis is a venereal disease of cattle characterized primarily by early fetal death and infertility, resulting in extended calving intervals. Distribution is likely worldwide. Diagnosis is confirmed by isolation of the organism. Imidazoles have been used to treat infected bulls, but none is both safe and effective. Control is by culling infected bulls.
Prolapse of the uterus may occur in any species; however, it is most common in dairy and beef cows and ewes and less frequent in sows. Uterine prolapse is rare in mares, bitches, queens, and rabbits. Invagination of the tip of the uterus, excessive traction to relieve dystocia or retained fetal membranes, uterine atony, hypocalcemia, and lack of exercise have all been incriminated as contributory causes. In sheep, grazing estrogenic pastures may also be a contributing factor.
Eversion and prolapse of the vagina, with or without prolapse of the cervix, occurs most commonly in cattle and sheep (cows and ewes) and usually occurs in mature animals in the last trimester of pregnancy. A form of vaginal prolapse also occurs in dogs.
Contusion and hematoma of the vagina occur after parturition in all species but especially in mares and sows. Occasionally, vaginal hematomas in sows may rupture and cause serious hemorrhage that can be controlled by ligation of the labial branch of the internal pudendal artery. Necrotic vaginitis, vestibulitis, and vulvitis may follow dystocia in all species. Onset of clinical signs, including an arched back, elevated tail, anorexia, straining and dysuria, vulvar and perivulvar swelling, and sometimes a foul-smelling serous vaginal discharge, occurs within 1–4 days of parturition and may persist for 2–4 weeks. In most cases, only medical treatment is needed. Frequently, antimicrobial prophylaxis is indicated, because clostridial or other organisms may proliferate in the affected tissues, resulting in tetanus, blackleg, or other forms of clostridial myositis. Potential sequelae of necrotic vaginitis include perivaginal abscessation, transvaginal adhesions and permanent vaginal strictures.
Although dogs occasionally become infected with Brucella abortus, B suis, or B melitensis, these sporadic occurrences typically are closely associated with exposure to infected domestic livestock (All.see page Brucellosis in Large Animals).
Tumors arising from mammary tissue are commonly observed in older, intact female dogs and cats. A mammary tumor is usually suspected on detection of a mass during physical examination in the caudal abdominal and cranial thoracic mammary glands (in dogs and cats, respectively). The diagnosis is confirmed by histopathology and is important for determining treatment and prognosis. Surgical removal of the tumor with the regional lymph node will increase disease-free time but, in cases of malignancy, may not increase survival time.
Disease of the prostate gland is relatively common in intact dogs but less common in other domestic animal species. Benign prostatic hyperplasia is by far the most common disease of the prostate in intact male dogs. Bacterial prostatitis (acute or chronic), prostatic abscesses, prostatic and paraprostatic cysts, and prostatic adenocarcinoma are seen much less frequently and can be seen in castrated males.
Canine transmissible venereal tumors (TVTs) are cauliflower-like, pedunculated, nodular, papillary, or multilobulated in appearance. They range in size from a small nodule (5 mm) to a large mass (>10 cm) that is firm, though friable. The surface is often ulcerated and inflamed and bleeds easily. TVTs may be solitary or multiple and are almost always located on the genitalia. The tumor is transplanted from site to site and from dog to dog by direct contact with the mass. They may be transplanted to adjacent skin and oral, nasal, or conjunctival mucosae.